The present invention relates to control devices for nail hitting of pneumatic nail guns, and particularly to a control device capable of controlling nail hitting action of nail guns according to thickness of workpiece.
Currently, pneumatic nail guns are widely used to join a workpiece (for example, a gasket) onto an object with a nail. The workpiece may include a through hole preformed on it. The users must align a nail with the through hole and then press the nail into the through hole and the object to fix the workpiece. To reduce difficulty of aligning, people developed a nail gun exposing a tip of the nail outside the nail gun.
In addition, different workpieces have different thickness. To provide ability of automatically detecting workpieces that are in predetermined thickness range in pneumatic nail guns, conventionally, the pneumatic nail includes a safety rod installed in a main passageway. The main passageway usually connects a trigger valve and a main valve. The safety rod includes a positioning member formed at a bottom end. When the safety rod reaches a predetermined height above the object, a control valve conducts pressurized air to open the main valve; as a result, the pressurized air drives a drive rod to hit the nail. The predetermined height includes a thickness of the workpiece or a depth of the through hole. The user can place a tip of the nail exposed from a drive track exit in the through hole. The tip is in contact with a surface of the object. The positioning member is sustained by the workpiece, and the depth of the through hole is reflected by a relative distance between the tip and the positioning member. When a height of the positioning member is in a predetermined range, the control valve conduct pressurized air to switch the main valve to an open state, and then the pressurized air drives the drive rod to hit the nail.
US Patent Publication No. 20070075113 discloses a pneumatic nail gun having a control device for nail hitting action, which employs a swinging pole and a valve stem. A safety rod can drive the swinging pole. The swinging pole can block or release the valve stem. In other words, the safety rod can control blocking or releasing of the valve stem. As a result, the safety rod can also control the mail valve to open to start press nail. However, the valve stem is directly controlled by the pressurized air, the stability is relative low. Also, the swinging pole is located between the valve stem and the safety rod, and the structure is too complex. It is difficult to maintain stability of nail hitting action.
Further, Taiwan Patent Publication No. M312401 also discloses a pneumatic nail gun with a control device providing a safety design for hitting action. The nail gun has a hollow valve bolt driven or released by a safety rod, and a valve cover which can exhaust the pressurized air to the outer atmosphere through opening or closing the main air flow passage controlled by the valve bolt. The safety rod is first driven to move up to block the valve bolt. The high pressure air in the main air flow passage is then exhausted to the outer atmosphere by pulling the trigger. The main air valve can be controlled to hit nails. However, the passage configuration between the hollow valve bolt and the valve cover is complicated; resulting in adequate air in the main air chamber and the main air flow passage, thus the stability of the nail gun is insufficient.